The use of decorative laminates in furniture and kitchen cabinetry has grown steadily for many years. Modified melamine resins have sufficient flow at low pressures when impregnated into cellulose paper sheets to be bonded directly to wood particleboard, cured and discharged from the press while still hot. Such products have been in commercial use in Europe for many years and are now being introduced in large volume in many other parts of the world. Sometimes called low pressure laminates, they are more descriptively called decorative faced boards. Decorative faced boards are engineered to provide prefinished decorative vertical surfacing components for the kitchen cabinet, furniture, fixture and mobile home industries.
A typical board may consist of a 65 lb. (3,000 sq. ft./ream) print or decorative sheet impregnated with about 60% to 65% melamine/formaldehyde resin which is bonded to a particleboard (from 3/8" to 3/4" in thickness) at a pressure of about 250-400 psi in 40 to 90 seconds at about 325.degree.-450.degree. F. Both sides of the particleboard must be covered to prevent warpage and one or both particleboard faces may carry a decorative sheet. The warpage preventing layer opposite the primary decorative surface is called a balance sheet. Some constructions will carry a resin impregnated translucent overlay above the decorative sheet in order to impart a harder surface to the decorative faced board. Subsequent to the pressing of the large size board, it will be cut into smaller panels for shipment to ultimate users. Some users will perform additional operations on a panel such as drilling holes, inserting cutouts for hardware or edgebanding the panel with matching laminate strips.
The surfaces of these decorative boards are hard and non-absorbent and, therefore, are not suitable for subsequent gluing to other structural members or to other decorative boards because the resulting bond is poor. The strength of the bond may be improved by sanding or otherwise roughening the surfaces to be united, but there are a number of disadvantages to such a treatment. For example, sanding is wasteful and is apt to introduce variations in thickness of the glue layer and a non-uniform bond strength throughout the board. Moreover, the decorative surface may be damaged by the sanding process. Furthermore, by sanding one side of a decorative board, stresses may be created which may cause the board to warp.
Furthermore, in many service applications, the consumer may desire to paint the interior surface of a board which has been formed into a useful article e.g. a kitchen cabinet. For the same reasons as described above with regard to the gluing problems associated with these boards, painting the boards is also a problem because of poor adhesion.